Primary document research is different than relying upon research conducted by someone else.
Using web based services you can do some verification of facts but my experience has been that primary document research has been necessary to solve the trickier questions. Inconsistencies in spelling of names, ages that don’t line up and divorces make electronic research all the more tricky.
A secondary benefit of primary document research is that you may come across other beneficial information. For example you may find an electronic reference that someone was divorced. You can simply rely on that fact or you can dig a little deeper and get the divorce records from the court. With that additional primary research you may get many additional clues about where they lived, status of children, household wealth and in my case clarification of names and prior addresses.
A great deal of information is available electronically although vast amounts have yet to be scanned and indexed and remain on dusty shelfs in city / county offices.